1. Field of the Invention
This invention is directed to a method of making a large refractory article, and in particular, large refractory blocks or forming bodies, such as an isopipe used in the manufacture of glass.
2. Technical Background
Large refractory articles (e.g. blocks) are often used in the manufacture of glass due to their superior resistance to the high temperatures experienced in the process, and the harsh chemical nature of molten glass. These articles are typically formed by first forming a green refractory body, then heating, or firing, the green body to drive off any moisture, burn off organic binders that might be present, and densify the body by causing individual particles comprising the body to coalesce. This densification is accompanied by shrinking or contraction of the body, wherein the final sintered article is smaller than the original green body (e.g. the length of the article decreases).
The frictional forces between a small green body and the structure supporting the green body within the furnace or kiln are not so great that excessive stress is introduced into the body during the shrinkage of the body. However, for large bodies, frictional forces can create large stress in the body. In some applications, the final sintered article is massive (e.g. having a mass in excess of 450 kg), and frictional forces can result in induced stresses that can fracture the body, either during the sintering, or later when the sintered article is used. For sintered articles having a mass much larger than 450 kg, the ability to sinter the precursor green body is significantly compromised, i.e. there is a increasing tendency for the sintering to produce cracks in the body. Thus, there is a need for a method of making large refractory bodies that can accommodate large contractions of the body during the sintering process and does not induce high stresses in the body or the resultant sintered article than can produce cracks or other stress-related flaws.